Apparatuses for the crankpin diameter checking of a crankshaft rotating with orbital motion about a geometric axis in the course of the machining in a grinding machine are disclosed in international patent application published with No. WO-A-9712724, filed by the same applicant of the present patent application.
More specifically, according to the embodiments shown and described in the previously detailed international patent application, the apparatuses have Vee-shaped reference devices that rest on the crankpin to be checked and maintain correct cooperation with the surface of the crankpin substantially by virtue of the force of gravity.
The embodiments disclosed in the formerly detailed international patent application guarantee excellent metrological results and small forces of inertia and the standards of performance of the apparatuses with these characteristics, manufactured by the applicant of the present patent application, confirm the remarkable quality and reliability of the applications.
Furthermore, these known apparatuses can be utilized for carrying out roundness checkings of the cylindrical surfaces of the pins, while the crankshaft is assembled and rotating on the grinding machine.
International patent application published with No. WO-A-0166306, also filed by the same applicant of the present patent application, relates to an apparatus and a method for checking the roundness of crankpins in orbital rotation on a grinding machine. This international patent application discloses the detecting of diameter dimensions of the crankpin, at predetermined angular positions during the crankshaft rotation, by means of a gauging head including a feeler and Vee-shaped reference surfaces that rest on the piece and a transducer that detects displacements of the feeler along a direction of measurement coincident with the bisecting line of the Vee or slightly sloping with respect to it.
The detected dimensions are processed for both compensating distorsions due to the geometric features of the particular type of head used (modulation of the shape errors of the checked surface that is in contact with the reference Vee) and carrying out other compensations for keeping into account the position taken by the head on the surface of the crankpin, more specifically the angular arrangement of the instantaneous point of contact of the feeler with respect to a known reference, that depends on the relative arrangement between the support element and the crankshaft and on the characteristics and consequent configurations taken by the support device carrying the head. FIGS. 1a and 1b show, in an extremely simplified form, some parts of an apparatus according to the previously detailed patent application published with No. WO-A-0166306, coupled to the grinding-wheel slide of a grinding machine, in the course of checkings of a cylindrical crankpin. In order to evidence how the angular arrangement of the measurement direction D defined by feeler T depends on the mutual position between the piece to be checked and the coupling area of the apparatus, FIGS. 1a and 1b show two different checking conditions. In the first condition (FIG. 1a) the apparatus checks the pin while the latter is in contact with the grinding wheel, in the second condition (FIG. 1b) the grinding-wheel slide is retracted from the piece. Consideration should also be given to the fact that, in the course of the checking of a pin in orbital motion (for example a crankpin), variations in the configuration of the support device cause consequent variations in the angular arrangement of the feeler.
The method according to international patent application published with No. WO-A-0166306 enables to achieve excellent results notwithstanding the unavoidable approximations due to the various processings that depend on the theoretic behavior of the involved mechanic component parts.
International patent application published with No. WO-A-02070195, also filed by the same applicant of the present patent application, illustrates and describes apparatuses that can as well be utilized for checking the dimensions and the roundness of pins in orbital rotation on a grinding machine and have the characteristics detailed at the beginning of the present description. More specifically, the disclosed apparatuses include coupling mechanisms carrying the Vee-shaped device, with movable coupling elements that enable substantially translation displacements of the Vee-shaped device with respect to the support element.
FIGS. 2a and 2b show, in simplified form, an apparatus according to international patent application published with No. WO-A-02070195, coupled to the grinding-wheel slide of a grinding machine, in the course of checkings of a cylindrical crankpin. It is possible to notice that the angular arrangement of the measurement direction D, along which feeler T translates, does not vary as the configuration taken by the coupling mechanism varies, the latter having coupling elements defining, for example, two parallelogram structures. This enables to know—beforehand and regardless of the reciprocal position between support element and workpiece to be checked—the angular position of the instantaneous point of contact at which the feeler touches the surface of the piece to be checked. In this way in the event it is required to utilize the apparatus for performing, for example, roundness checkings, at least part of the processings of the detected values—required for checkings carried out with the apparatuses known, for example, from international patent application published with No. WO-A-0166306—are not necessary, and this enables, among other things, to minimize the approximations in the calculations and provide more rapid and reliable checking operations.